The present invention relates generally to methods for uplink power control for satellite/wireless networks. More specifically, the present invention relates to methods for uplink power control for distributed satellite/wireless networks which compensate for rain fade and other equipment impairments. In addition, the present invention relates to methods for dynamically determining the power compression point for distributed satellite/wireless networks.
Wireless and Satellite networks have evolved over the years. Network architectures have evolved from star topologies supporting fixed private line voice and data to full-mesh systems for emerging ATM, Frame Relay, and ISDN traffic. Therefore, the network nodes have varying uplink capabilities that are optimized for cost and performance. Networks have also evolved in complexity. Older networks traditionally used static bandwidth management schemes. Today's networks allocate bandwidth on demand, i.e., bandwidth is continuously changing while the network is carrying traffic. To minimize cost, the earth station transmit amplifiers are selected to deliver the rated power close to saturation, without an overly conservative built-in margin. However, the output of most of the commercially available amplifiers tends to degrade in terms of spectral side-lobe and shoulder regrowth when operated close to or in saturation. Therefore, the solutions developed should work in a power limited Bandwidth-On-Demand environment and meet stringent specifications for spectral regrowth.
Several approaches to material issues have been developed over the years. Two of the more popular algorithms that have been used for UPC are in star topology Very Small Aperture Terminal (VSAT) systems and Mobile Cellular systems. Traditional VSAT systems employ open-loop methods for UPC. Link quality measurements are performed on the same local downlink associated with the transmitter, using actual carrier signals or satellite beacons. An estimate of the uplink fade is derived from these downlink measurements and the transmit power is adjusted. In contrast, terrestrial cellular systems typically measure link quality of the mobile transmitter in a base station and feedback corrections to achieve a target link quality.
Both these methods operate on a single point-to-point transmit-receive pair basis. Very often, current methods require a wide power control dynamic range, and may drive the transmitter to operate in saturation, especially with changes over time and temperature.
Moreover, U.S. Pat. No. 5,619,525 to Wiedeman et al., for example, discloses a method of operating a satellite communication system, which method provides adaptive closed loop power control. First, the ground station transmits an uplink reference signal with a first frequency to the satellite. The uplink reference signal experiences an attenuation between the ground station and the satellite due to, for example, a rain cell. The satellite then receives the reference signal and repeats the reference signal at a second frequency as a downlink reference signal that is transmitted from the satellite. The second frequency is less than the first frequency and is not significantly impaired or attenuated by the rain cell. The downlink reference signal is transmitted with a power that is a function of the power of the received uplink reference signal. Then, the downlink reference signal is received and used to determine the amount of attenuation that was experienced at least by the uplink reference signal between the ground station and the satellite. Thereafter, the transmitted power of the uplink reference signal is adjusted in accordance with the determined amount of attenuation so as to substantially compensate for the experienced attenuation. It would be preferable to avoid such complexities.
Thus, the problem of UPC has been addressed extensively for traditional fixed star/mesh topology networks. However, existing solutions do not meet the needs of a Bandwidth-On-Demand satellite network with diverse earth station configurations. Currently used methods do not ensure link quality between every dynamically varying transmit/receive pair on a burst-basis. Some of the current approaches may drive transmit amplifiers into an operating region that increases spectral sidelobe/shoulder regrowth. Such methods usually allocate a huge link margin that increases the transmit amplifier power requirement and hence drives up the cost. Operating transmitters with a large built-in margin consumes excess satellite transponder power and decreases available transponder bandwidth capacity.
What is need is an UPC method which correctly discriminates between rain or impairments on the uplink or downlink when overall link quality degrades. Moreover, what is needed is a method for power control which is capable of adapting to the varying traffic in Bandwidth-On-Demand networks wherein the bandwidth to different destinations from each node is continuously changing. In short, what is needed is an UPC method for compensating for uplink fade and degradations, when needed, in a mesh network of various earth stations.